This invention relates to monolithic microelectronic array structures and, more particularly, to a monolithic microelectronic array structure formed on discontinuous substrate islands.
Many imaging sensor systems utilize an optical system to focus the infrared or visible-light energy of a scene onto a detector array. One widely used detector array is the focal plane array (FPA), in which an array of detector elements is positioned at the focal plane of the optical system. The infrared or visible-light energy focused onto the detector elements is converted to electrical signals. The electrical signals indicative of the image are viewed on a display or processed by a computer, as for example with pattern recognition techniques.
There are two commonly used types of FPA detector element arrays. The most sensitive FPA detector arrays are hybrid detector array structures that use an optimized detector array and an optimized readout integrated circuit, with the respective detector arrays and the readout integrated circuits joined by an electrical interconnect structure in the form of metallic bumps. A less sensitive FPA detector array is a monolithic microelectronic array structure formed of an array of readout circuit elements deposited on a substrate with a detector element directly connected to each of the readout circuit elements. In each case, the detector elements of the detector array are arranged to define pixels of an image and convert the incident infrared or visible-light energy to output electrical signals. The respective readout integrated circuits amplify and condition the electrical signals for subsequent use.
The present invention relates to monolithic microelectronic array structures. Although the monolithic microelectronic array structures are less sensitive than the hybrid detector array structures when used as light detectors, the monolithic microelectronic array structures have important applications such as in uncooled man-portable night vision systems that must operate uncooled at ambient temperature, be less costly to produce, and consume less power than the hybrid detector array structures.
Monolithic microelectronic array structures of several types are available and are widely used in focal plane arrays. However, the present inventors have recognized that available monolithic microelectronic array structures have limitations on their geometries and performance. Certain geometries of imaging sensor systems that would otherwise be highly advantageous cannot be made with available monolithic microelectronic array structures. Some of the same problems arise with light-emitter arrays such as diode or laser arrays, and with other types of microelectronic integrated circuit arrays.
There is therefore a need for an improved monolithic microelectronic array structure. The present invention fulfills this need, and further provides related advantages.
The present invention provides a monolithic microelectronic array structure and a method for its fabrication. The monolithic microelectronic array structure may be made in a planar or curved form. In either a planar (flat) or curved form, there is a mechanical isolation between the microelectronic integrated circuit elements that reduces the incidence of thermal strains and stresses. When in a curved form, the monolithic microelectronic array structure may be conformed to a nonplanar focal surface that allows the construction of microelectronic systems not heretofore possible.
In accordance with the invention, a monolithic microelectronic array structure comprises a microelectronic integrated circuit array comprising a first plurality of substantially identical microelectronic integrated circuit elements, each deposited on a front side of one of a plurality of substrates. The substrates are physically discontinuous so that each substrate comprises a substrate island which is physically separated from the other substrate islands. There is a second plurality of electrically conductive, structurally flexible interconnects extending between the microelectronic integrated circuit elements of adjacent substrate islands.
In one embodiment, each microelectronic integrated circuit element comprises an electrical interface circuit and an input/output element supported on the electrical interface circuit. The electrical interface circuit may be a readout integrated circuit, and the input/output element is a detector of light. The electrical interface circuit may be a driver integrated circuit, and the input/output element is an emitter of light.
The monolithic microelectronic array structure may be substantially planar. In another form made possible by the segmented structure of the islands and the interconnects, the monolithic microelectronic array structure is curved in single or double curvature. Desirably, each electrically conductive interconnect is structurally flexible. In one form, each electrically conductive interconnect between two adjacent islands is curved in a perpendicular plane that is perpendicular to an extrapolated intersection line between the two islands it connects. In another form, each electrically conductive interconnect between two islands is curved in an included plane that includes an extrapolated intersection line between the two islands it connects.
In a typical case, each substrate is made of a substantially inflexible material such as a piece of silicon. Although the substrate islands are physically separated from each other, there may be a continuous flexible support to which a back side of each substrate island is affixed.
The substrate islands may have exactly one readout integrated circuit element on each substrate island. They may instead have more than one readout integrated circuit element on each substrate island.
A method for preparing a monolithic microelectronic array structure includes providing an initial structure comprising a planar physically continuous substrate, and a first plurality of microelectronic integrated circuit elements each deposited on a front side of the planar physically continuous substrate. A second plurality of electrically conductive interconnects is deposited to extend between adjacent microelectronic integrated circuit elements. The method further includes trenching the planar physically continuous substrate from a back side thereof to form a trenched structure and to physically separate the planar physically continuous substrate into a first plurality of physically discontinuous substrate islands with at least one of the electrically conductive interconnects extending between each adjacent substrate island. This trenched structure may be used flat, or it may be deformed into a curved structure in the event that the electrically conductive interconnects are structurally flexible. Other features of the structure may be provided as described above.
When used as a detector, the structure of the monolithic microelectronic array may be advantageously employed in a singly (e.g., a segment of a cylindrical surface) or doubly (e.g., a segment of a spherical surface) curved form, or a complexly curved form. The curved monolithic detector array is positioned as a focal surface array (comparable to a focal plane array or FPA, except that it is not planar) at a similarly curved focal surface of an imaging sensor system. Such a curved focal surface approach offers particular advantages for compact, wide-angle sensors (or emitters), which have not heretofore been possible.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.